Regardless of glass capillary composition (most frequently soft or borosilicate glass, or fused silica), elimination of surface active sites is fundamentally important if maximum efficiency and applicability are to be achieved in the finished column. In this respect, the prior art has only been partly successful in developing satisfactory deactivation procedures, and the procedures which have been developed are often narrowly limited in success.
Probably the most widely applied of the prior art methods of capillary surface deactivation are those processes involving acid leaching the capillary inner surface which increases the density of the surface hydroxyl groups. This is followed by reacting the acid-leached surface with silylating reagents, commonly methylchlorosilanes, whereby the active hydroxyl groups are replaced by inert silyl-ether groups. Generally high reactive temperatures are required for proper silylation (e.g., about 400.degree. C. or greater). In addition, the selection of the silylating reagent, its concentration, distribution in the capillary column, temperature and time are all highly critical parameters in these prior art processes, as described by Godefroot et al., Journal of HRC and CC, Vol. 3, July 1980, pp. 337-344). Despite strictest adherence to process variable control, Godefroot et al. observed difficulty with these procedures in reproducing uniform capillary columns, and caution that the results which are obtained are to be treated as strictly limited. Grob et al., Journal of HRC and CC, Vol. 3, April, 1980, pp. 197, 198, similarly observe that high temperature silylation surface deactivation is difficult to control and described the processes in terms of results as achieving only limited success. Nevertheless, Grob et al. judge the current high temperature silylating procedures, despite the serious limitations reported as being "the most efficient way (known) to produce very inert columns."
The invention in response to these problems provides improved glass and fused silica capillaries in which highly improved surface deactivation results are produced by bonding to the glass or silica a thin, inactive surface film of siloxane polymer molecules. Used in conjunction with apolar polymer film coatings, capillaries prepared by this new procedure demonstrate significantly lower residual surface activities than their commercially available counterparts, have much improved thermal stability, and are reasonably simple to reproducibly prepare via safe laboratory practices.